Colin Bignell <cpb@bignellremovethis.me.uk> wrote:
> On 23/04/2023 18:35, Chris Green wrote:
> > Colin Bignell <cpb@bignellremovethis.me.uk> wrote:
> >>>>
> >>>> The whole point of it was to be able to cut larger holes than most hole
> >>>> saw sets could manage. From memory, the arm was about eight inches long,
> >>>> but I don't recall having to cut anything more than about six inches
> >>>> diameter. I wouldn't be surprised if it wasn't something my father had
> >>>> made up years before.
> >>>>
> >>> Not practical for cutting a hole in the side of my boat I don't think!
> >>>
> >>
> >> I think it would be possible, but take quite a while to cut through 5mm
> >> steel. You would get a very neat hole though.
> >>
> >> Have you asked whether your local tool hire has a power nibbler capable
> >> of dealing with 5mm mild steel?
> >>
> > I don't know if the French are into tool hire (the boat is in France),
> > I've never noticed any tool hire places. It's an idea though, I'll
> > hunt around a bit.
> >
>
> Some Bricomarché stores do tool hire. Also look for "location
> d'outillage" or "location d'outils.
>
Yes, thanks, I tried "location d'outils" immediately after your
original suggestion and there are a couple of possibles locally. I
haven't yet really investigated that hard to see if they have anything
like plasma cutters.

Strangely there isn't a Bricomarché anywhere near, we have a
Leroy-Merlin close and a Brico-Depot not too far away, but that's all.

--
Chris Green
·

On 23/04/2023 12:27, Colin Bignell wrote:
> On 23/04/2023 10:55, nothanks@aolbin.com wrote:
>> On 23/04/2023 10:13, Colin Bignell wrote:
>>> On 22/04/2023 14:34, Chris Green wrote:
>>>> I need to replace a porthole on our little boat because the existing
>>>> one has bad corrosion around it.  So I need to enlarge the hole from
>>>> the existing 8" to about 10".
>>>>
>>>> The porthole is simply mounted in a hole in the 5mm steel
>>>> superstructure, what can I cut it with?  I can cut straight lines in
>>>> steel with a cutting disk in my angle grinder but I don't know what to
>>>> do for cutting curves.
>>>>
>>>> I suppose a jigsaw might manage it but it would have to be a good one
>>>> with good blades, both my current jigsaws are pretty ropey.
>>>>
>>>> So, is there any other way to do this that I haven't thought of? Or
>>>> can anyone recommend a jigsaw and blades that will cut through 30" of
>>>> 5mm steel without too much effort (or cost!).
>>>>
>>>> This is probably just going to be one off requirement so I don't mind
>>>> spending a bit more time to avoid having to buy anything I'm not going
>>>> to use much.
>>>>
>>>
>>> Amazon does a 10 inch hole saw. It says it is only for thin metals,
>>> but back it off, cool it down and lubricate well and it might manage
>>> 5mm steel.
>>>
>>>
>> Not possible without a centre ... that's why I proposed stitch drilling
>
> As I suggested elsewhere in the thread, a piece of ply on each side of
> the hole, with screws holding them together in the existing hole and you
> have a centre.
Apologies, I didn't spot that ... but ply isn't going to cope with the
side loads caused by jams when going through 5mm. Also, I really
wouldn't fancy trying to use a 10" hole saw in a hand drill to go
through 5mm steel. A while ago I badly injured my wrist when a 16mm bit
jammed when drilling-out a gate hinge - and that was only using a high
torque battery drill.
If the surface is flat it *might* be possible to use a hired mag drill
(Rotabroach?) - I've used them to make holes in an RSJ (for pipes and
cables), but not 10" diameter!
If 't'were me I'd stitch drill, as I described earlier, with decent
sharp drill bits and some oil.

PS The "single tooth cutting bit, mounted on an arm" that you mentioned
is called a fly cutter - very useful but it's a brave (foolish?) person
that tries to use one hand-held.>
> I remember my father stitch drilling holes to make rounded corners for
> windows he was putting in the back of a van (he had to pay £5 tax to
> convert it). It was a long and laborious job, even in thin steel bodywork.
>
>

On 24-Apr-23 14:53, nothanks@aolbin.com wrote:
> On 23/04/2023 14:49, Fredxx wrote:
>> On 23/04/2023 13:49, Colin Bignell wrote:
>>> On 23/04/2023 13:30, nothanks@aolbin.com wrote:
>>>> On 23/04/2023 12:27, Colin Bignell wrote:
>>>>> On 23/04/2023 10:55, nothanks@aolbin.com wrote:
>>>>>> On 23/04/2023 10:13, Colin Bignell wrote:
>>>>>>> On 22/04/2023 14:34, Chris Green wrote:
>>>>>>>> I need to replace a porthole on our little boat because the
>>>>>>>> existing
>>>>>>>> one has bad corrosion around it.  So I need to enlarge the hole
>>>>>>>> from
>>>>>>>> the existing 8" to about 10".
>>>>>>>>
>>>>>>>> The porthole is simply mounted in a hole in the 5mm steel
>>>>>>>> superstructure, what can I cut it with?  I can cut straight
>>>>>>>> lines in
>>>>>>>> steel with a cutting disk in my angle grinder but I don't know
>>>>>>>> what to
>>>>>>>> do for cutting curves.
>>>>>>>>
>>>>>>>> I suppose a jigsaw might manage it but it would have to be a
>>>>>>>> good one
>>>>>>>> with good blades, both my current jigsaws are pretty ropey.
>>>>>>>>
>>>>>>>> So, is there any other way to do this that I haven't thought of? Or
>>>>>>>> can anyone recommend a jigsaw and blades that will cut through
>>>>>>>> 30" of
>>>>>>>> 5mm steel without too much effort (or cost!).
>>>>>>>>
>>>>>>>> This is probably just going to be one off requirement so I don't
>>>>>>>> mind
>>>>>>>> spending a bit more time to avoid having to buy anything I'm not
>>>>>>>> going
>>>>>>>> to use much.
>>>>>>>>
>>>>>>>
>>>>>>> Amazon does a 10 inch hole saw. It says it is only for thin
>>>>>>> metals, but back it off, cool it down and lubricate well and it
>>>>>>> might manage 5mm steel.
>>>>>>>
>>>>>>>
>>>>>> Not possible without a centre ... that's why I proposed stitch
>>>>>> drilling
>>>>>
>>>>> As I suggested elsewhere in the thread, a piece of ply on each side
>>>>> of the hole, with screws holding them together in the existing hole
>>>>> and you have a centre.
>>>> Apologies, I didn't spot that ... but ply isn't going to cope with
>>>> the side loads caused by jams when going through 5mm. Also, I really
>>>> wouldn't fancy trying to use a 10" hole saw in a hand drill to go
>>>> through 5mm steel. A while ago I badly injured my wrist when a 16mm
>>>> bit jammed when drilling-out a gate hinge - and that was only using
>>>> a high torque battery drill.
>>>> If the surface is flat it *might* be possible to use a hired mag
>>>> drill (Rotabroach?) - I've used them to make holes in an RSJ (for
>>>> pipes and cables), but not 10" diameter!
>>>> If 't'were me I'd stitch drill, as I described earlier, with decent
>>>> sharp drill bits and some oil.
>>>
>>> I would hate to have to try that for a 10" circle in 5mm steel. It
>>> would take forever. I suspect an oxy-acetylene cutter would be the
>>> easiest way to do it.
>>
>> Stitch drill is a last ditch method where you don't have a jig-saw. I
>> cannot recommend it. It would take ages, and take longer cleaning the
>> edge up with an angle grinder.
>>
>> I recommend you look up plasma cutters. Obviously you need a mains
>> power supply as they take quite a bit of power. They are incredibly
>> cheap to run.
>>
>> Then on down to oxy-propane, oxy-propylene and then oxy-acetylene.
>>
>>
>>
> I haven't used plasma cutters but am prepared to believe that they would
> do the job. However, everyone has a drill and not everyone has access to
> a plasma cutter (etcetera) and the skills to use it safely and
> effectively. There are many exotic tools that might make a particular
> job easier or quicker, but if you ain't got one or don't know how to use
> it then finding a way to use what you have becomes the better approach.

Hmm. 10 inch circle, 5mm steel.
How many holes would be needed, and hence how many drill bits would you
get through in doing the job?
The wear & tear on the drill is another factor.

--
Sam Plusnet

On 24/04/2023 22:51, Sam Plusnet wrote:
> On 24-Apr-23 14:53, nothanks@aolbin.com wrote:
>> On 23/04/2023 14:49, Fredxx wrote:
>>> On 23/04/2023 13:49, Colin Bignell wrote:
>>>> On 23/04/2023 13:30, nothanks@aolbin.com wrote:
>>>>> On 23/04/2023 12:27, Colin Bignell wrote:
>>>>>> On 23/04/2023 10:55, nothanks@aolbin.com wrote:
>>>>>>> On 23/04/2023 10:13, Colin Bignell wrote:
>>>>>>>> On 22/04/2023 14:34, Chris Green wrote:
>>>>>>>>> I need to replace a porthole on our little boat because the
>>>>>>>>> existing
>>>>>>>>> one has bad corrosion around it.  So I need to enlarge the hole
>>>>>>>>> from
>>>>>>>>> the existing 8" to about 10".
>>>>>>>>>
>>>>>>>>> The porthole is simply mounted in a hole in the 5mm steel
>>>>>>>>> superstructure, what can I cut it with?  I can cut straight
>>>>>>>>> lines in
>>>>>>>>> steel with a cutting disk in my angle grinder but I don't know
>>>>>>>>> what to
>>>>>>>>> do for cutting curves.
>>>>>>>>>
>>>>>>>>> I suppose a jigsaw might manage it but it would have to be a
>>>>>>>>> good one
>>>>>>>>> with good blades, both my current jigsaws are pretty ropey.
>>>>>>>>>
>>>>>>>>> So, is there any other way to do this that I haven't thought
>>>>>>>>> of? Or
>>>>>>>>> can anyone recommend a jigsaw and blades that will cut through
>>>>>>>>> 30" of
>>>>>>>>> 5mm steel without too much effort (or cost!).
>>>>>>>>>
>>>>>>>>> This is probably just going to be one off requirement so I
>>>>>>>>> don't mind
>>>>>>>>> spending a bit more time to avoid having to buy anything I'm
>>>>>>>>> not going
>>>>>>>>> to use much.
>>>>>>>>>
>>>>>>>>
>>>>>>>> Amazon does a 10 inch hole saw. It says it is only for thin
>>>>>>>> metals, but back it off, cool it down and lubricate well and it
>>>>>>>> might manage 5mm steel.
>>>>>>>>
>>>>>>>>
>>>>>>> Not possible without a centre ... that's why I proposed stitch
>>>>>>> drilling
>>>>>>
>>>>>> As I suggested elsewhere in the thread, a piece of ply on each
>>>>>> side of the hole, with screws holding them together in the
>>>>>> existing hole and you have a centre.
>>>>> Apologies, I didn't spot that ... but ply isn't going to cope with
>>>>> the side loads caused by jams when going through 5mm. Also, I
>>>>> really wouldn't fancy trying to use a 10" hole saw in a hand drill
>>>>> to go through 5mm steel. A while ago I badly injured my wrist when
>>>>> a 16mm bit jammed when drilling-out a gate hinge - and that was
>>>>> only using a high torque battery drill.
>>>>> If the surface is flat it *might* be possible to use a hired mag
>>>>> drill (Rotabroach?) - I've used them to make holes in an RSJ (for
>>>>> pipes and cables), but not 10" diameter!
>>>>> If 't'were me I'd stitch drill, as I described earlier, with decent
>>>>> sharp drill bits and some oil.
>>>>
>>>> I would hate to have to try that for a 10" circle in 5mm steel. It
>>>> would take forever. I suspect an oxy-acetylene cutter would be the
>>>> easiest way to do it.
>>>
>>> Stitch drill is a last ditch method where you don't have a jig-saw. I
>>> cannot recommend it. It would take ages, and take longer cleaning the
>>> edge up with an angle grinder.
>>>
>>> I recommend you look up plasma cutters. Obviously you need a mains
>>> power supply as they take quite a bit of power. They are incredibly
>>> cheap to run.
>>>
>>> Then on down to oxy-propane, oxy-propylene and then oxy-acetylene.
>>>
>>>
>>>
>> I haven't used plasma cutters but am prepared to believe that they
>> would do the job. However, everyone has a drill and not everyone has
>> access to a plasma cutter (etcetera) and the skills to use it safely
>> and effectively. There are many exotic tools that might make a
>> particular job easier or quicker, but if you ain't got one or don't
>> know how to use it then finding a way to use what you have becomes the
>> better approach.
>
> Hmm.  10 inch circle, 5mm steel.
> How many holes would be needed, and hence how many drill bits would you
> get through in doing the job?
> The wear & tear on the drill is another factor.
>
Simples! (I think!) 10" diameter is 254mm. Assume a 10mm drill bit so
PCD is 244mm and drilling circumference is about 760mm. Assume 2mm gap
between holes so about 64 holes needed. So, at 5 mm thickness, that's
about a total drilling depth of 320 mm ... not too bad.
It may need a couple of drill bits (depending on whether the optimum
speeds and oil are used) but wear on a decent drill will be
insignificant. I'd guess at about an hour.

On 25/04/2023 00:09, nothanks@aolbin.com wrote:
> On 24/04/2023 22:51, Sam Plusnet wrote:
>> On 24-Apr-23 14:53, nothanks@aolbin.com wrote:
>>> On 23/04/2023 14:49, Fredxx wrote:
>>>> On 23/04/2023 13:49, Colin Bignell wrote:
>>>>> On 23/04/2023 13:30, nothanks@aolbin.com wrote:
>>>>>> On 23/04/2023 12:27, Colin Bignell wrote:
>>>>>>> On 23/04/2023 10:55, nothanks@aolbin.com wrote:
>>>>>>>> On 23/04/2023 10:13, Colin Bignell wrote:
>>>>>>>>> On 22/04/2023 14:34, Chris Green wrote:
>>>>>>>>>> I need to replace a porthole on our little boat because the
>>>>>>>>>> existing
>>>>>>>>>> one has bad corrosion around it.  So I need to enlarge the
>>>>>>>>>> hole from
>>>>>>>>>> the existing 8" to about 10".
>>>>>>>>>>
>>>>>>>>>> The porthole is simply mounted in a hole in the 5mm steel
>>>>>>>>>> superstructure, what can I cut it with?  I can cut straight
>>>>>>>>>> lines in
>>>>>>>>>> steel with a cutting disk in my angle grinder but I don't know
>>>>>>>>>> what to
>>>>>>>>>> do for cutting curves.
>>>>>>>>>>
>>>>>>>>>> I suppose a jigsaw might manage it but it would have to be a
>>>>>>>>>> good one
>>>>>>>>>> with good blades, both my current jigsaws are pretty ropey.
>>>>>>>>>>
>>>>>>>>>> So, is there any other way to do this that I haven't thought
>>>>>>>>>> of? Or
>>>>>>>>>> can anyone recommend a jigsaw and blades that will cut through
>>>>>>>>>> 30" of
>>>>>>>>>> 5mm steel without too much effort (or cost!).
>>>>>>>>>>
>>>>>>>>>> This is probably just going to be one off requirement so I
>>>>>>>>>> don't mind
>>>>>>>>>> spending a bit more time to avoid having to buy anything I'm
>>>>>>>>>> not going
>>>>>>>>>> to use much.
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Amazon does a 10 inch hole saw. It says it is only for thin
>>>>>>>>> metals, but back it off, cool it down and lubricate well and it
>>>>>>>>> might manage 5mm steel.
>>>>>>>>>
>>>>>>>>>
>>>>>>>> Not possible without a centre ... that's why I proposed stitch
>>>>>>>> drilling
>>>>>>>
>>>>>>> As I suggested elsewhere in the thread, a piece of ply on each
>>>>>>> side of the hole, with screws holding them together in the
>>>>>>> existing hole and you have a centre.
>>>>>> Apologies, I didn't spot that ... but ply isn't going to cope with
>>>>>> the side loads caused by jams when going through 5mm. Also, I
>>>>>> really wouldn't fancy trying to use a 10" hole saw in a hand drill
>>>>>> to go through 5mm steel. A while ago I badly injured my wrist when
>>>>>> a 16mm bit jammed when drilling-out a gate hinge - and that was
>>>>>> only using a high torque battery drill.
>>>>>> If the surface is flat it *might* be possible to use a hired mag
>>>>>> drill (Rotabroach?) - I've used them to make holes in an RSJ (for
>>>>>> pipes and cables), but not 10" diameter!
>>>>>> If 't'were me I'd stitch drill, as I described earlier, with
>>>>>> decent sharp drill bits and some oil.
>>>>>
>>>>> I would hate to have to try that for a 10" circle in 5mm steel. It
>>>>> would take forever. I suspect an oxy-acetylene cutter would be the
>>>>> easiest way to do it.
>>>>
>>>> Stitch drill is a last ditch method where you don't have a jig-saw.
>>>> I cannot recommend it. It would take ages, and take longer cleaning
>>>> the edge up with an angle grinder.
>>>>
>>>> I recommend you look up plasma cutters. Obviously you need a mains
>>>> power supply as they take quite a bit of power. They are incredibly
>>>> cheap to run.
>>>>
>>>> Then on down to oxy-propane, oxy-propylene and then oxy-acetylene.
>>>>
>>>>
>>>>
>>> I haven't used plasma cutters but am prepared to believe that they
>>> would do the job. However, everyone has a drill and not everyone has
>>> access to a plasma cutter (etcetera) and the skills to use it safely
>>> and effectively. There are many exotic tools that might make a
>>> particular job easier or quicker, but if you ain't got one or don't
>>> know how to use it then finding a way to use what you have becomes
>>> the better approach.
>>
>> Hmm.  10 inch circle, 5mm steel.
>> How many holes would be needed, and hence how many drill bits would
>> you get through in doing the job?
>> The wear & tear on the drill is another factor.
>>
> Simples! (I think!) 10" diameter is 254mm. Assume a 10mm drill bit so
> PCD is 244mm and drilling circumference is about 760mm. Assume 2mm gap
> between holes so about 64 holes needed.

How are you going to get past the remaining 120mm of steel (64 x 2mm)?

A jig-saw?

> So, at 5 mm thickness, that's
> about a total drilling depth of 320 mm ... not too bad.
> It may need a couple of drill bits (depending on whether the optimum
> speeds and oil are used) but wear on a decent drill will be
> insignificant. I'd guess at about an hour.

And the rest. If going down that route I might start at 3mm before
moving to 10mm diameter.

Still think jig-saw is the best route if there's no other method.

Fredxx wrote:

> Still think jig-saw is the best route if there's no other method.

Less likely to set the boat on fire than a plasma cutter ...

Andy Burns <usenet@andyburns.uk> wrote:
> Fredxx wrote:
>
> > Still think jig-saw is the best route if there's no other method.
>
> Less likely to set the boat on fire than a plasma cutter ...
>
OP here, it has been known! Not with a plasma cutter but....

A few years ago the boat was having an extra steel skin fixed to its
hull because corrosion had thinned the original hull. I was inside
monitoring things but not quite well enough, some expanded polystyrene
(horrible stuff, I've removed just about all of it now) caught fire and I
wasn't able to extinguish it immediately. Fortunately the shipyard were
*very* switched on, I got out and there were guys with breathing
apparatus and extinguishers there within a minute or so.

It was a bit black and smokey around the area that had caught fire but
there was little permananent damage, just some clearing up.

I monitored inside the boat even more carefully while they were
welding after that!

--
Chris Green
·

On Saturday, 22 April 2023 at 14:48:08 UTC+1, Chris Green wrote:
> I need to replace a porthole on our little boat because the existing
> one has bad corrosion around it. So I need to enlarge the hole from
> the existing 8" to about 10".
>
> The porthole is simply mounted in a hole in the 5mm steel
> superstructure, what can I cut it with? I can cut straight lines in
> steel with a cutting disk in my angle grinder but I don't know what to
> do for cutting curves.
>
> I suppose a jigsaw might manage it but it would have to be a good one
> with good blades, both my current jigsaws are pretty ropey.
>
> So, is there any other way to do this that I haven't thought of? Or
> can anyone recommend a jigsaw and blades that will cut through 30" of
> 5mm steel without too much effort (or cost!).
>
> This is probably just going to be one off requirement so I don't mind
> spending a bit more time to avoid having to buy anything I'm not going
> to use much.
>
> --
> Chris Green
> ·
A gas axe?

On 22/04/2023 16:59, Colin Bignell wrote:
> On 22/04/2023 16:33, Fredxx wrote:
>> On 22/04/2023 15:57, Colin Bignell wrote:
>>> On 22/04/2023 14:34, Chris Green wrote:
>>>> I need to replace a porthole on our little boat because the existing
>>>> one has bad corrosion around it.  So I need to enlarge the hole from
>>>> the existing 8" to about 10".
>>>>
>>>> The porthole is simply mounted in a hole in the 5mm steel
>>>> superstructure, what can I cut it with?  I can cut straight lines in
>>>> steel with a cutting disk in my angle grinder but I don't know what to
>>>> do for cutting curves.
>>>>
>>>> I suppose a jigsaw might manage it but it would have to be a good one
>>>> with good blades, both my current jigsaws are pretty ropey.
>>>>
>>>> So, is there any other way to do this that I haven't thought of? Or
>>>> can anyone recommend a jigsaw and blades that will cut through 30" of
>>>> 5mm steel without too much effort (or cost!).
>>>>
>>>> This is probably just going to be one off requirement so I don't mind
>>>> spending a bit more time to avoid having to buy anything I'm not going
>>>> to use much.
>>>>
>>>
>>> I used to have a tool that would cut variable diameter holes in
>>> steel. It comprised a single tooth cutting bit, mounted on an arm.
>>> The arm passed through a spindle, where it was held by a screw, so
>>> that the diameter could be adjusted. Very effective, quite dangerous
>>> and best used at slow speed. However, it needed a pilot hole to run
>>> in, so you would need to do something like screw a couple of pieces
>>> of ply together, on either side of the steel, putting the screws
>>> through the existing hole, then put the pilot hole through those, in
>>> the centre of your new hole. The cutting bit would also need to be
>>> long enough to cut through one layer of play plus the steel.
>>
>> A 10 inch diameter hole? 5 inch arm?
>>
>> How many rpm are we talking about?
>
> The slowest speed on our pillar drill, which I think was 50 or 60 rpm.
>
> Sorry, it doesn't seem feasible
>> except for small diameter holes.
>
> The whole point of it was to be able to cut larger holes than most hole
> saw sets could manage. From memory, the arm was about eight inches long,
> but I don't recall having to cut anything more than about six inches
> diameter. I wouldn't be surprised if it wasn't something my father had
> made up years before.
>
> I have, however, got a similar, commercially made, cutter for putting
> holes through ceilings for PAR 38 downlighters, but that comes with a
> built-in rubbish catcher and is intended for use with a hand drill.
>
>

Reads from the description, like a 'tank cutter'.

On 25/04/2023 21:45, Harry Bloomfield Esq wrote:
> On 22/04/2023 16:59, Colin Bignell wrote:
>> On 22/04/2023 16:33, Fredxx wrote:
>>> On 22/04/2023 15:57, Colin Bignell wrote:
>>>> On 22/04/2023 14:34, Chris Green wrote:
>>>>> I need to replace a porthole on our little boat because the existing
>>>>> one has bad corrosion around it.  So I need to enlarge the hole from
>>>>> the existing 8" to about 10".
>>>>>
>>>>> The porthole is simply mounted in a hole in the 5mm steel
>>>>> superstructure, what can I cut it with?  I can cut straight lines in
>>>>> steel with a cutting disk in my angle grinder but I don't know what to
>>>>> do for cutting curves.
>>>>>
>>>>> I suppose a jigsaw might manage it but it would have to be a good one
>>>>> with good blades, both my current jigsaws are pretty ropey.
>>>>>
>>>>> So, is there any other way to do this that I haven't thought of? Or
>>>>> can anyone recommend a jigsaw and blades that will cut through 30" of
>>>>> 5mm steel without too much effort (or cost!).
>>>>>
>>>>> This is probably just going to be one off requirement so I don't mind
>>>>> spending a bit more time to avoid having to buy anything I'm not going
>>>>> to use much.
>>>>>
>>>>
>>>> I used to have a tool that would cut variable diameter holes in
>>>> steel. It comprised a single tooth cutting bit, mounted on an arm.
>>>> The arm passed through a spindle, where it was held by a screw, so
>>>> that the diameter could be adjusted. Very effective, quite dangerous
>>>> and best used at slow speed. However, it needed a pilot hole to run
>>>> in, so you would need to do something like screw a couple of pieces
>>>> of ply together, on either side of the steel, putting the screws
>>>> through the existing hole, then put the pilot hole through those, in
>>>> the centre of your new hole. The cutting bit would also need to be
>>>> long enough to cut through one layer of play plus the steel.
>>>
>>> A 10 inch diameter hole? 5 inch arm?
>>>
>>> How many rpm are we talking about?
>>
>> The slowest speed on our pillar drill, which I think was 50 or 60 rpm.
>>
>> Sorry, it doesn't seem feasible
>>> except for small diameter holes.
>>
>> The whole point of it was to be able to cut larger holes than most
>> hole saw sets could manage. From memory, the arm was about eight
>> inches long, but I don't recall having to cut anything more than about
>> six inches diameter. I wouldn't be surprised if it wasn't something my
>> father had made up years before.
>>
>> I have, however, got a similar, commercially made, cutter for putting
>> holes through ceilings for PAR 38 downlighters, but that comes with a
>> built-in rubbish catcher and is intended for use with a hand drill.
>>
>>
>
> Reads from the description, like a 'tank cutter'.

TNP reminded me of the name fly cutter, but tank cutter seems to be the
same thing.

--
Colin Bignell

On 25-Apr-23 9:21, Chris Green wrote:
> Andy Burns <usenet@andyburns.uk> wrote:
>> Fredxx wrote:
>>
>>> Still think jig-saw is the best route if there's no other method.
>>
>> Less likely to set the boat on fire than a plasma cutter ...
>>
> OP here, it has been known! Not with a plasma cutter but....
>
> A few years ago the boat was having an extra steel skin fixed to its
> hull because corrosion had thinned the original hull. I was inside
> monitoring things but not quite well enough, some expanded polystyrene
> (horrible stuff, I've removed just about all of it now) caught fire and I
> wasn't able to extinguish it immediately. Fortunately the shipyard were
> *very* switched on, I got out and there were guys with breathing
> apparatus and extinguishers there within a minute or so.
>
> It was a bit black and smokey around the area that had caught fire but
> there was little permananent damage, just some clearing up.
>
> I monitored inside the boat even more carefully while they were
> welding after that!
>

Did the same shipyard do the Admiral Kuznetsov? In Murmansk?

--
Sam Plusnet

Colin Bignell wrote:

> Harry Bloomfield wrote:
>
>> Reads from the description, like a 'tank cutter'.
>
> TNP reminded me of the name fly cutter, but tank cutter seems to be the
> same thing.

I thought a fly cutter was a multi carbide-tipped tool for surfacing
using a milling machine, rather than for making holes?

I've got a sort-of tank cutter for making holes in plasterboard ceilings
to fit recessed lights (i.e. bigger than downlighters) even that is a
bit sketchy to use.

On 26/04/2023 09:26, Andy Burns wrote:
> Colin Bignell wrote:
>
>> Harry Bloomfield wrote:
>>
>>> Reads from the description, like a 'tank cutter'.
>>
>> TNP reminded me of the name fly cutter, but tank cutter seems to be
>> the same thing.
>
> I thought a fly cutter was a multi carbide-tipped tool for surfacing
> using a milling machine, rather than for making holes?
>
A fly cutter is simply a single cutter on an adjustable radius arm. You
can use it to mill or drill

A tank cutter is the same as a hole saw, but generally for metal

> I've got a sort-of tank cutter for making holes in plasterboard ceilings
> to fit recessed lights (i.e. bigger than downlighters) even that is a
> bit sketchy to use.
>
>

--
The higher up the mountainside
The greener grows the grass.
The higher up the monkey climbs
The more he shows his arse.

Traditional

On Sat, 22 Apr 2023 15:03:38 +0100, Andy Burns <usenet@andyburns.uk> wrote:

>I'd have thought a jigsaw with decent blades and take it steady would do
>the job, if it finishes either or both of them off ... well you've got a
>chance to treat yourself to a new one!

Gonna piggyback upthread here...

When using a jigsaw, a piece of wood under the jigsaw base plate can help: with
5mm steel, and the usual jigsaw stroke, there's only a bit of the jigsaw blade
being used. Pack a spacer under the jigsaw, perhaps with a slot to guide the
blade. This allows using fresh teeth further on down on the blade, so you get
more cut length out of one blade before it is dull...

Thomas Prufer

On 26/04/2023 13:51, Thomas Prufer wrote:
> On Sat, 22 Apr 2023 15:03:38 +0100, Andy Burns <usenet@andyburns.uk> wrote:
>
>> I'd have thought a jigsaw with decent blades and take it steady would do
>> the job, if it finishes either or both of them off ... well you've got a
>> chance to treat yourself to a new one!
>
> Gonna piggyback upthread here...
>
> When using a jigsaw, a piece of wood under the jigsaw base plate can help: with
> 5mm steel, and the usual jigsaw stroke, there's only a bit of the jigsaw blade
> being used. Pack a spacer under the jigsaw, perhaps with a slot to guide the
> blade. This allows using fresh teeth further on down on the blade, so you get
> more cut length out of one blade before it is dull...
>
> Thomas Prufer

A good tip, thanks.

--
Cheers
Clive

On 26/04/2023 13:53, Clive Arthur wrote:
> On 26/04/2023 13:51, Thomas Prufer wrote:
>> On Sat, 22 Apr 2023 15:03:38 +0100, Andy Burns <usenet@andyburns.uk>
>> wrote:
>>
>>> I'd have thought a jigsaw with decent blades and take it steady would do
>>> the job, if it finishes either or both of them off ... well you've got a
>>> chance to treat yourself to a new one!
>>
>> Gonna piggyback upthread here...
>>
>> When using a jigsaw, a piece of wood under the jigsaw base plate can
>> help: with
>> 5mm steel, and the usual jigsaw stroke, there's only a bit of the
>> jigsaw blade
>> being used. Pack a spacer under the jigsaw, perhaps with a slot to
>> guide the
>> blade. This allows using fresh teeth further on down on the blade, so
>> you get
>> more cut length out of one blade before it is dull...
>>
>> Thomas Prufer
>
> A good tip, thanks.
>
+1

--
In a Time of Universal Deceit, Telling the Truth Is a Revolutionary Act.

- George Orwell

On 26/04/2023 13:51, Thomas Prufer wrote:
> On Sat, 22 Apr 2023 15:03:38 +0100, Andy Burns <usenet@andyburns.uk> wrote:
>
>> I'd have thought a jigsaw with decent blades and take it steady would do
>> the job, if it finishes either or both of them off ... well you've got a
>> chance to treat yourself to a new one!
>
> Gonna piggyback upthread here...
>
> When using a jigsaw, a piece of wood under the jigsaw base plate can help: with
> 5mm steel, and the usual jigsaw stroke, there's only a bit of the jigsaw blade
> being used. Pack a spacer under the jigsaw, perhaps with a slot to guide the
> blade. This allows using fresh teeth further on down on the blade, so you get
> more cut length out of one blade before it is dull...

I'm not sure that's worth the effort?

The stroke of the jig-saw will be far more than 5mm (say 15mm stroke?)
so the proportion of blade having been used will still be quite high.
While you might get a clean few mm of blade after using removing a shim,
you'll then be overlapping the heavily used part of the blade too.

I think I would buy an extra blade!

On Wed, 26 Apr 2023 14:11:16 +0100, Fredxx <fredxx@spam.uk> wrote:

>The stroke of the jig-saw will be far more than 5mm (say 15mm stroke?)
>so the proportion of blade having been used will still be quite high.
>While you might get a clean few mm of blade after using removing a shim,
>you'll then be overlapping the heavily used part of the blade too.
>
>I think I would buy an extra blade!

5 mm steel + 15 mm stroke leaves plenty on a blade that has at least 40 mm
usable length.

The blade does get more wobbly towards the tip -- and this is a tip for when you
don't have an unlimited supply of extra blades.

Thomas Prufer